Make 'em growl?

[rleete]

I was watching various steam/air/IC engine videos on the web last night. Found a bunch of familiar names and engines along the way.

Anyway, I was looking for engines that have a particular sound to them. The Liney Halo demo video was one example. Those engines, that when throttled up sound like a particularly quiet version of a "real" engine. The ones that, instead of a continuous psssssst sound, have a distinct and sometimes a little throaty exhaust note. Most of the larger radials had it, but there were exceptions as well. None of the ones I saw appeared to have any kind of exhaust piping or manifolds to tailor the sound.

So, how do you accomplish it? Is there a rule of thumb for making the exhaust more realistic? Is it simply a function of pressure, or cylinder bore or something else?

 

[Blogwitch]

I designed and put one of these on my little engine, and it really increased the sound output.

http://www.homemodelenginemachinist.com/index.php?topic=536.0

As you can hear in this vid


[ame]http://www.youtube.com/watch?v=76FAAv-PB78[/ame]


Bogs

 

[Lakc]

Nice work there Bogs

There are a lot of variables that go into the way an engine sounds, cam timing, exhaust shape, and exhaust gas velocity are probably the most important ones.

 

[cidrontmg]

Most steam engine exhausts are just a hole in the valve box (or a hole in the oscillator stand), so the exhaust note (beat) is more or less what it happens to be. There´s no reason why you couldn´t add a "silencer" (hehe..), or a resonator, to modify the beat. A big volume, heavy-walled chamber, fed with a small exhaust hole, will get a deeper (more bassy) thudding, a thin-walled small reso type pipe will result in a higher pitched whine (with a higher-revving engine, of course, surely not with a beam engine...). Nothing better than experimenting. But many people want their engines to sound like a sewing machine, i.e. as little exhaust beat as possible. Nothing wrong with that line of thinking either.

Funny you should mention Liney Halo. I´m (s l o w l y) building one, to double size (linear). It runs already, but not too good. Still lots of work with the cylinder heads. Anyway, the Halo (original) exhausts are just holes in the head (ehrm...), but I´ve added some curved exhaust pipes. They´re more for the looks, but they also improve the exhaust sound a lot (that is, I like it more. Funky deep growl ;D ).

 

[rleete]

Bogs, you wouldn't happen to have any vid of the same engine without that device for comparison?

I remember the post, and had at one time tried to make one, but it didn't seem to have very much affect on my single cylinder oscillator. Guess I'm going to have to try some things and see what helps.

 

[Blogwitch]

R,

This is without the 'chuffer'

[ame]http://www.youtube.com/watch?v=SpjTo8o7d6E[/ame]

You need to experiment to get the sound you want, different lengths and diameters change the pitch dramatically. Mine was 'tuned' to make my engine sound how I wanted it to be. If you really wanted to, you could mount a whistle or a whizzer on there, you would hear it then.

Cid,

I too am building some Halos (when I eventually get back to them), and mine will be fitted with a short megaphone type, just to increase the 'bark' of the exhaust.


Bogs

 

[cidrontmg]

Cid,

I too am building some Halos (when I eventually get back to them), and mine will be fitted with a short megaphone type, just to increase the 'bark' of the exhaust.

Bogs

Heh, just what I was thinking also... The Halo has a nice growl as it is, same as most radials. But there´s always room for improvement, aesthetic and phonetic. Somehow the exhaust "holes in the head" just don´t seem adequate. And they would smear the next head with oil...